A collapsible core for molding parts is disclosed in U.S. Patent Application US 2006/0188602. That patent discloses a two-sleeve collapsible core device for molding articles around the core device in a mold cavity. The first sleeve includes a plurality of first ribs extending from a first base in an axial direction and defining a discontinuous first perimeter surrounding a channel. The second sleeve includes a plurality of second ribs extending from a second base in an axial direction and defining a discontinuous second perimeter surrounding the central channel. Each of the second ribs is arranged between adjacent ones of the first ribs. The expansion member is fittable within the central channel to displace the first and second ribs outwardly to form an overall perimeter defined by the first and second ribs.
In practice, the expansion member is slightly tapered or rounded at an end thereof to prevent friction based wear on the central channel when the expansion member is inserted into the central channel to displace the sleeve rib members outward. The expansion member forms the top part of the molding surface. The rounded end of the expansion member prevents the outer top edge of the expansion member from being flush with the tops of the sleeve rib members. If the expansion member is inserted to the extent that it is flush with tops of the sleeve rib members, the rounded edge and the top of the expansion member must extend a small amount above the tops of the sleeve rib members. Therefore, the expansion member creates an indention or impression on the resulting molded surface. However an expansion member with a non-tapered or non-rounded end could cause undue wear on the central channel.
The present inventor recognizes that it would be desirable to provide a collapsible core assembly that does not cause an indentation or impression in the molded surface, but also wherein the expansion member does not cause undue friction and wear on the central channel when the expansion member is inserted into the central channel.